1xe2x80x94Field of the Invention
The invention relates to a system for rotationally coupling two telescopic shafts along their common axis. A coupling system in accordance with the invention can in particular be applied to an automobile vehicle steering column, adopting it for an intermediate column part connected to a steering box or for an upper column part connected to a steering wheel.
2xe2x80x94Description of the Prior Art
In the more particular case of the intermediate shaft, the latter has a universal joint at each end: one universal joint is connected to a motion input of the steering box and the other universal joint is connected to the column top portion. To steer present-day automobile vehicles correctly, it is necessary for the length of the intermediate shaft to be variable and to adapt to oscillations of the front wheels of the vehicle, which oscillations are caused by the profile and state of the road surface.
Thus the intermediate shaft must first of all have a variable length, i.e. it must have a function of sliding of two shafts relative to each other along their common axis, which is the axis of the intermediate part. It must also have a function of transmission between the two shafts of rotation motion and the rotation torque necessary for operating the steering.
There are many sliding shaft coupling systems which transmit rotation torque between the two shafts by means of splines which have conjugate profiles respectively on the two shafts.
However, it is difficult to make this type of system with on the one hand a sufficient angular stiffness and on the other hand a sufficiently accurate axial displacement force in the event of an impact.
The object of the present invention is to propose a telescopic shaft coupling system that avoids the foregoing drawbacks, i.e. a system which in normal operation functions with no clearance and which can transmit the very high rotation torque in exceptional operation. The system for coupling the two shafts must also be easy to install in the available spaces of existing automobile vehicles.
The invention concerns a system for rotationally coupling two shafts able to turn about a common axis. One of the two shafts is an interior shaft and the other shaft is an exterior shaft, the two shafts being disposed so that they can slide one within the other along said common axis. According to the invention, the coupling system comprises:
a first rotational coupling between the two shafts and which is constituted by a rotation friction system between the interior shaft and the exterior shaft; and
a second rotational coupling between the two shafts and which is constituted by internal splines and external splines, the internal splines extending on the periphery of the end of the interior shaft and the external splines extending on the internal face of a tube constituting the exterior shaft, the internal splines and the external splines being adapted to cooperate with each other so that if a normal rotation torque is to be transmitted it is transmitted by friction and if an exceptional rotation torque is to be transmitted it is additionally transmitted by the splines after taking up clearance between the splines.
In one particularly advantageous embodiment of the invention, the first rotational coupling between the interior shaft and the exterior shaft includes a spring ring which constitutes the rotation friction system, and said spring ring on the one hand is pressed onto an internal face of a housing in the exterior shaft and on the other hand is pressed onto a smooth or knurled portion of an external face of the interior shaft.
In the above embodiment, the following highly beneficial architecture of the spring ring is used. Said spring ring is a metal ring which has a slit over the whole of its axial length. Said metal ring has over the whole of its circular length internal axial recesses and external axial recesses. The recesses alternate so that an external axial recess follows on from an internal axial recess. The external axial recesses are pressed onto the internal face of the housing in the exterior shaft, and the internal axial recesses are pressed onto the smooth or knurled portion of the external face of the interior shaft.
Furthermore, the coupling system according to the invention can include an axial coupling between the interior shaft and the exterior shaft.
In this case, the axial coupling between the interior shaft and the exterior shaft is effected by the rotation friction system, which is adapted to resist axial sliding between the interior shaft and the exterior shaft up to a predetermined value.
To further improve the performance of the coupling system according to the invention, said system includes a one-way axial abutment system to prevent extraction of the interior shaft in the direction of the common axis. Said axial abutment system includes a toroidal ring which is disposed in a housing located at an end of the exterior shaft and which is retained in the direction of the common axis by a crimping folding at said end of the exterior shaft on the toroidal ring, and said toroidal ring is pressed onto the smooth portion of the external face of the interior shaft.
The coupling system according to the invention applied to an intermediate portion of an automobile vehicle steering column or to a top portion of an automobile vehicle steering column.
The system for rotationally coupling two telescopic shafts thus has the advantage that it transmits rotation torque with no clearance under normal operating conditions and guarantees transmission of rotation torque under exceptional operating conditions. Finally, the coupling system can easily be installed in the space available for steering columns in existing automobile vehicles.